Method of making wire



y 8, 1963 J. s. HILL ET AL 3,091,026

METHOD OF MAKING WIRE Filed Nov. 13, 1958 2 GROUPING 4 SINTERING 5 HOTWORKING 6 GOLD WORKING IN VEN T 0R5 ATTORN EY United States Patent3,091,026 METHOD OF MAKING WIRE James S. Hill, Cranford, N.J., and CecilS. Sivil, deceased, late of East Orange, N.J., by Blanche 0. Sivil,executrix, East Orange, N.J., assignors, by mesne assignments, toEngelhartl Industries, Inc, Newark, N .J., a corporation of DelawareFiled Nov. 13, 1958, Ser. No. 773,637 3 Claims. (Cl. 29-419) The presentinvention deals with a method of making wire and more particularly witha method of making Wire for high temperature applications and especiallyfor use as thermocouple Wire and furnace windings.

Certain metals, such as metals of the platinum group, eg. platinum,palladium, rhodium, in substantially pure state are used as hightemperature electrical conductors in view of the ability of such metalsto withstand high temperatures. The pure metals are, nevertheless,subject to grain growth and brittleness under prolonged use under hightemperatures. The grain growth progresses with prolonged use untilcontinuous grain boundaries completely traverse the diameter of the wireand some slippage occurs along the grain boundary resulting in a changein electrical characteristics or breakage of the wire at the grainboundary.

It is an object of the present invention to provide a method of makingwire of substantially pure metal, whereby grain growth is retarded andmechanical strength is maintained under conditions which would otherwisedeleteriously affect the wire. It is another object of the invention toprovide a method making wire of pure metal, whereby desirable electricalcharacteristics thereof are maintained under prolonged use at hightemperatures. Other objects and advantages of the invention will becomeapparent from the description hereinafter following and the drawingsforming a part hereof, in which:

FIGURE 1 illustrates a perspective view of a Wire,

FIGURE 2 illustrates a perspective view of a modified form of wire,

FIGURE 3 illustrates a perspective view of a compact bundle oflongitudinally aligned wires,

FIGURE 4 illustrates a longitudinal sectional view of FIGURE 3, but withthe ends of the bundled Wire fused into a solid mass, and

FIGURE 5 illustrates a diagrammatic illustration of the method stepsemployed in the making of a wire according to the invention.

The invention relates to the method of making a wire from a bundle ofindividual wires of substantially pure metal, the bundle being compactedand sintered at a temperature above the recrystallization temperature ofthe wire metal and subsequently hot worked to a solid wire mass.Thereafter, the wire is worked to desirable dimensions by the usualalternating hot and cold working.

More specifically, and according to the illustrations, a plurality ofwires 1, for example wires of circular crosssection, or wires 2 ofrectangular cross-section are first cleaned by usual cleaning methods toremove foreign or undesirable material on the surfaces thereof, and suchwires are grouped into a bundle 3 as illustrated by FIG- URE 3. Thewires are cleaned, e.g. by etching with an acid prior to grouping into acompact bundle and secured or maintained in the form of a bundle bymechanical clamping or, preferably, by fusing the ends of the wires asat 4 and 5 into a solid mass. The compact bundle is then sintered at atemperature above the recrystallization temperature of the metal untilthe individual wires are bonded together into a rod. The sintered orfrittered bundle 3 is worked by hot rolling until it is in the form of ahot metal rod as one solid mass. Thereafter, the metal rod is coldworked to desired dimensions or alter 3,991,026 Patented May 28, 1963 2i nately cold Worked and hot worked until the desired dimensions areattained.

Eicample Wires of chemically pure platinum having a square cross-sectionof 0.110" were etched with aqua regia until the surfaces thereof werechemically clean. Ninety-nine of the wires were grouped and compactedinto a bundle 1" square. Both ends of the bundle were heat-treated witha helium electric arc until the individual wire ends were fused into asolid mass. The fusion of the ends of the bundle secured the bundle as acompact group. The secured bundle was placed in a furnace andheattreated at a temperature of 1400 C. (which is above therecrystallization temperature and below the melting temperature of theplatinum) for 16 hours until the individual wires were bonded into theform of a solid rod. The bonded rod was then hot worked at 1000 C. byrolling between a pair of shaped reducing rolls and hot rolled to asquare cross-section of 0.625. At this reduction the individual Wireswere not distinguishable and the rod was in the form of a solid metalmass. The rod was further reduced by cold rolling to a 0.110 squarecrosssection, and still further reduced by drawing to finished size,i.e. 0.020". A four foot length of the wire was connected between a pairof electrodes and electric power was passed through the wire for eighthours continuously at 287 watts. After 8 hours, a micrographiccross-section showed no crystals large enough to traverse the wirecross-section and with the metal crystals being highly irregular andinterlocked.

A four foot length of conventional platinum wire Was tested underidentical conditions and showed grains developed across the entirecross-section of the wire.

Stress rupture tests showed that the wire of the invention showed a lifetest of one hundred times that of the convenional platinum wire, bothwires consisting of chemically pure platinum.

The stress rupture tests were conducted at a temperature of 1400 C.under a load of 230 lbs/sq. in.

It has been determined that the method of manufacturing wire accordingto the invention creates a migration of various occlusions in the metalto the grain boundaries where the occlusions become fixed and act toretard grain growth. In conventional Wire, there is a minimum ofocclusions, but in the wire of the invention, an increase of occlusionsis created by the method of manufacture, whereby the metal is still inthe pure state and of desirable electrical characteristics together withincreased mechanical strength, which are maintained under use of thewire at high temperatures.

While the example is specific to platinum, other substantially puremetals can be formed into wire by the method of the invention within thescope of the appended claims.

What is claimed is:

1. The method of making electrically conductive graingrowth controlledwire for use in high temperature operating devices comprising chemicallycleaning numerous Wires of substantially the same size and of the samesubstantially pure metal selected from the class consisting of platinum,palladium and rhodium, grouping and securing the wires into a compactbundle, heat treating the bundle at a temperature above therecrystallization temperature and below the melting temperature of themetal until the wires are bonded into a rod reducing the cross-sectionof the rod by hot working until the rod is a solid metal mass ofsubstantially pure metal, and cold working the rod into wire.

2. The method according to claim 1, wherein the hot working comprisesreducing the cross-section thereof by hot rolling.

3 4 3. The method according to claim 1, wherein the cold 2,234,127Mautsch Mar. 4, 1941 Working comprises drawing the rod into wire.2,691,815 Boessenkool et a1. Oct. 19, 1954 2,753,623 Boessenkool et a1.July 10, 1956 References Cited in the file of this patent 2, 42,440Nachtman et 1 J l 1953 N ED STATES PATENTS 5 2.984.89 Hil y 1961 369,144WilliQIIlSOH Aug. 30, 1887 OTHER REFERENCES 504,431 Green Sept. 5, 1893623,652 Carta APR 25, 1399 The Platinum Metels by M. W156, pages297-309, 1,307,054 King et aL June 17, 1919 published by InternationalNickel Co., New York, New 1,962,359 Dietz et a1 June 12 1934 10 York,and based upon chapter XV, Modern Uses of Non- 2206395 Gamer July 2,1940 ferrous Metals, Second edition, 1953, A.I.M.E.

1. THE METHOD OF MAKING ELECTRICALLY CONDUCTIVE GRAIN GROWTH CONTROLLEDWIRE FOR USE IN HIGH TEMPERATURE OPERATING DEVICES COMPRISING CHEMICALLYCLEANING NUMEROUS WIRES OF SUBSTANTIALLY THE SAME SIZE AND OF THE SAMESUBSTANTIALLY PURE METAL SELECTED FROM THE CLASS CONSISTING OF PLATINUM,PALLADIUM AND RHODIUM, GROUPING AND SECURING THE WIRES INTO A COMPACTBUNDLE, HEAT TREATING THE BUNDLE AT A TEMPERATURE ABOVE THERECRYSTALLIZATION TEMPERATURE AND BELOW THE MELTING TEMPERATURE OF THEMETAL UNTIL THE WIRES ARE BONDED INTO A ROD REDUCING THE CROSS-SECTIONOF THE ROD BY HOT WORKING UNTIL THE ROD IS A SOLID METAL MASS OFSUBSTANTIALLY PURE METAL, AND COLD WORKING THE ROD INTO WIRE.